1. Field of the Invention
The present invention relates to a one-way clutch. More specifically, the present invention relates to an improvement in a sprag type one-way clutch of disengaging type.
2. Related Background Art
In general, one-way clutches in which an outer race is rotated are divided into a one-way clutch of engaging type attaching importance to an engaging ability and a one-way clutch of disengaging type attaching importance to low drag ability. Among them, the one-way clutch of disengaging type is designed so that, during engagement, when an inner race and an outer race are stopped or are rotated at a low speed, they are engaged by each other in an inner race driving fashion to transmit a power to the outer race, and, if over-run is generated at the outer race side, idle rotation occurs.
FIG. 4 shows a conventional one-way clutch of disengaging type, wherein, in a condition that a gravity center G of a sprag 23 is positioned at the left of a contact point A between the sprag 23 and an outer race 21, when a centrifugal force is generated, the sprag 23 is inclined toward a clockwise direction around the point A. Thus, a height of the sprag 23 is decreased, with the result that an inner race side cam surface of the sprag 23 is separated from a track surface of an inner race 22.
Further, a ribbon spring 27 serves to apply torque turning in an anti-clockwise direction to the sprag 23. When the outer race 21 is idly rotated in a direction shown by the arrow X at a high speed, the sprag 23 is more inclined toward the clockwise direction, and an inclined posture of the sprag 23 is maintained at a position where a rotational force obtained by the ribbon spring 27 is balanced with a rotational force obtained by the centrifugal force of the sprag 23. A one-way clutch of such type is disclosed in Japanese Patent Application Laid-open Nos. 2000-220663 and S63-285336 (1988).
However, in the conventional one-way clutch of disengaging type, due to vibration and/or rotational fluctuation during the high speed operation, the sprag is swung or fluctuated to apply repeated load to the ribbon spring, thereby causing fatigue damage of the ribbon spring and wear of a tip end of the ribbon spring which is contacted with the sprag.
In particular, when the one-way clutch is used as a starter of a motor bike, due to the vibration and/or rotational fluctuation during high speed idle rotation, the sprag is swung or fluctuated, with the result that a danger of damaging the ribbon spring of the one-way clutch may be increased.